1. Field of the Invention
The present invention concerns an apparatus for stretching, tightening, tensing and holding a sheet, e.g., a screen, a woven fabric, a tissue and/or another flat flexible substance or substrate. More particularly, the present invention is directed to stretching and holding screen printing screens to be used in screen printing.
2. Background Information
Prior to the invention of the present invention, screen, fabric, tissue and other material to be used in screen printing were stretched and held using one of the following devices and methods:
(1) Two inch by two inch pieces of wood were fastened at the ends to form 90.degree. corners forming a frame, the total dimensions of which were not important. A piece of screen material (fabric, etc.) was then stapled, glued or attached by other means along one side. The screen material was then pulled by hand or through the use of a device which clamps onto the screen and can be used to pull the material tight across the frame. Once the material is tight in one dimension, additional clamps were attached to pull in opposition to each other, perpendicular to the first clamp, thereby removing all wrinkles, while holding the screen material tight over the wooden frame. Once tight, the screen material was fastened, stapled etc. onto each of the remaining four sides of the frame, holding the screen tight for use in screen printing. PA1 (2) The Newman Roller Frame is an aluminum frame made to allow the user to retighten the screen after use. It works by first attaching the screen to the four sides that are made of round pipe material that is attached at the corners. A ratcheting device is employed such that the operator can tighten the screen by rotating the pipes, which pulls the screen tight in all directions. The Newman Roller Frame allows for superior tightening and retightening, but to use the same is time consuming and still does not allow the use an inexpensive alternative in saving the developed screens (the screen cannot be removed and reinstalled). PA1 a. a first planar frame having a first circumferential portion having a given first radial width, a given first axial depth, a first outer edge and a first inner edge, PA1 b. a second planar frame having a second circumferential portion having a given second radial width, a given second axial depth, a second outer edge and a second inner edge, PA1 c. a third planar frame having a third circumferential portion having a given third radial width, a given third axial depth, a third outer edge and a third inner edge, wherein the third inner edge extends radially inwardly of the first inner edge and the second inner edge, PA1 d. means for adhering a flexible sheet to one surface of the first planar frame, PA1 e. a stretching member attached to one surface of the third planar frame, the stretching member adjacent to the third inner edge and disposed radially inwardly of the first and second inner edges, the stretching member extending along the circumference of the third planar frame, and PA1 f. means for connecting the first, second and third frames together in a superposed relationship with the first frame disposed between the second frame and the third frame and the one surface of first frame facing the one surface of the third frame, wherein the stretching means has an axial depth such that when the three frames are connected together by the connecting means the sheet is stretched and held taut.
Various methods have been devised to tighten the screen prior to fastening to the wood frame, but each method has several disadvantages, such as the following: (A) It is cumbersome and difficult to stretch the screen and fasten the screen. It remains difficult in spite of the development of expensive pneumatic screen streching devices that have been made to stretch and fasten screen material to wooden frames automatically. (B) It is not possible, or extremely difficult to retighten the screen once it has been fastened. (C) If the screen is to be saved, it must be saved in its stretched form on the large wooden frame.
Prolonged use or storage of this conventional device will cause the sheet material to sag.